The overall goal of this project is to isolate and purify a population of osteoclasts suitable for detailed metabolic characterization. Tibiae of chicks maintained on a diet deficient in vitamin D provide an abundant source of osteoclasts. Osteoclasts from tibiae of chicks raised on a rachitogenic diet will be isolated using a nonenzymatic technique. The proximal portion of the tibia will be split lengthwise and the metaphyseal portion scraped out and placed in Ca-Mg-free Tyrodes solution. Osteoclasts will be dislodged by repeated flushing with this same solution. The initial isolate will be further purified by sequential filtration through Nitex cloth and sedimentation at unit gravity to increase the percentage of viable osteoclasts. The metabolic function of these osteoclasts will be monitored through oxygen consumption, glucose utilization and ATP production and the biochemical, hitochemical and ultrastructural features of these cells will be examined and compared to osteoclasts from D-replete chick tibiae. If differences between rachitic and normal osteoclasts are found, the manipulation of various ion (Ca and Pi) and hormonal (PTH and vitamin D metabolites) concentrations in vivo and in vitro will be tried to determine if the defect can be corrected. The functional ability of the isolated osteoclasts will be studied in depth to determine if they are able to attach to devitalized bone fragments in vitro. Their ability to form ruffled borders when stimulated with agents such as PTH and 1,25-(OH)2-D3 will be examined. Degradation of bone mineral and matrix will be assessed through release of previously incorporated 45Ca amd 3H- proline as well as by ultrastructural examination. Studies of isolated osteoclasts will contribute to a more complete understanding of their metabolism and their role in bone resorption. This will be of significant value in better understanding their role in periodontal disease as well as in normal bone remodeling.